Linebacker Tully Banta-Cain and special-teamer Keith Lewis were released by the 49ers on Tuesday, as speculation heated up about whether pricey offensive lineman Jonas Jennings would follow them out the door.

Jennings, 31, has played in just 23 of 64 games since signing a seven-year, $36 million contract in 2005. With the start of free agency looming on Feb. 27, the 49ers must consider whether it’s worth it to keep the oft-injured tackle on the roster. Cutting Jennings would save the 49ers about $3 million in salary cap space.

For now, the only official exits are Banta-Cain and Lewis, each of whom had one year remaining on their deals.

Banta-Cain was hailed as a boost to the 49ers pass rush when he arrived in 2007. Formerly a standout at Fremont High of Sunnyvale and Cal, he played all 16 games in his first season with the 49ers and set a career-high with 59 tackles, according to the coach’s statistics.

But he essentially vanished from the depth chart for parts of 2008 and finished with just 12 tackles.

Lewis, meanwhile, spent five seasons with the team after being drafted in the sixth round of the 2004 draft. A special-teams stalwart, Lewis started just 13 times in the secondary during his 49ers career and had not made a start since 2006.

Monday marked the first day that NFL teams could make waiver requests. Cutting Banta-Cain and Lewis saves the team about $2 million in salary-cap space.

ESPN.com estimates that the 49ers will have between $20 million to $30 million in what it calls “functional cap room” by the time free agency opens later this month.

Some of that figure depends on how the 49ers proceed with Jennings, whose 2008 season lasted just two games. He suffered a right-shoulder separation against Seattle on Sept. 14. After clinging to hope for a comeback, Jennings surrendered to surgery on Nov. 18 and was placed on injured reserve.

The 49ers had no comment about Jennings’ future Tuesday. At the time of the surgery, General Manager Scot McCloughan said only that Jennings’ status would be evaluated after the season.

McCloughan said of Jennings in November: “Everybody’s built different and some guys are more injury-prone than others, but there’s no reason why he can’t come back from this once rehab’s over and play again. There’s no reason, whatsoever.”

As the 49ers continue to gear up for free agency, they are also expected to renegotiate their deal for quarterback Alex Smith. McCloughan has said he wants the quarterback to remain on the roster, but only with a more salary-cap friendly contract. (Smith’s scheduled based salary for 2009 is close to $10 million).

The 49ers this week made a waiver claim on quarterback Bruce Gradkowski, formerly of Tampa Bay and Cleveland, but he was awarded instead to the Raiders because they had a worse record in 2008.